Many types of systems require one or more materials, e.g., gases, liquids, vapors, flowable particulates, etc., to be conveyed from one location to another, often within conduits, such as ducts and pipes. If the conveyed materials were innocuous to low-cost conduit materials, providing cost effective, durable conduit systems would be a simple matter. However, many conveyed materials have one or more characteristics that are detrimental to low-cost conduits. Therefore, materials that are resistant to the detrimental characteristics must be used to provide robust conveying systems. Examples of systems that carry materials detrimental to low-cost conduit materials include exhaust systems, e.g., microchip fabrication tool exhaust systems, fossil fuel power generation boiler flue gas exhaust systems, internal combustion engine exhaust systems, etc., and material supply and transfer systems, e.g., piping systems, for moving materials from one location to another for any of a variety of purposes.
In designing a conveyance system for a material having one or more detrimental characteristics, a designer generally has one or two options, depending upon the properties, e.g., strength, ductility, etc., of the material selected to resist the detrimental characteristic(s) of the conveyed material. For example, if the properties of the resistant material are such that an entire conduit can be constructed of that material, then the designer has the choice of either constructing the entire conduit out of the resistant material or constructing a large portion of the conduit out of a non-resistive material and utilizing the resistant material as a protective lining located between the conveyed material and the non-resistant material. The choice will often be driven by the cost and practicality of the resistant material. If the resistant material is relatively expensive, it may not be economical to construct an entire conduit out of that material. In this case, the designer would choose to only line the conduit with the resistant material. Of course, if the properties of the resistant material are such that the resistant material cannot practically be used to construct an entire conduit, e.g., the material is too weak, brittle or flexible, lining the conduit with the material may be the only way to provide the resistance needed. In addition, lined conduits are often desirable to provide fire-resistant conduit systems in which the conduits must maintain their structural integrity in the presence of unwanted fires within the conduits. In these cases, the lining materials resistant to the detrimental effect(s) of the conveyed material are typically flammable, so a fire-resistant material, such as steel, is used to support the lining and carry the structural loads imposed on, and by, the conduits.
An example of a system in which materials resistant to the detrimental effect(s) of conveyed materials are often utilized as linings is an exhaust system for a microelectronics chip material deposition tool, such as a chemical vapor deposition (CVD) apparatus. Over the years, a relatively efficient design has evolved for conduits, i.e., ducts, of such exhaust systems. Generally, this design is a lining-type design in which a fluoropolymer lining is applied to cylindrical duct segments each having a radial, outwardly turned flange at each end. Typically, the fluoropolymer lining is applied to the interior surfaces and the joint faces of the flanges using a conventional high-temperature bonding process. To form a run of duct, a plurality of duct segments are joined with one another by placing a gasket between the flanges of abutting duct segments and compressing the gasket between the flanges using one or more mechanical clamps. Other types of lined ducts are available, such as ducts made using flanged duct segments containing separate liners having turned-out ends that confront the joint faces of the flanges. Such a joint is shown in U.S. Pat. No. 4,127,287 to Davies. In this type of joint, the turned-out ends of the liner are compressed against one another between the flanges of abutting duct segments using mechanical clamps.
While the joints of these ducts have generally served the semiconductor fabrication and other industries relatively well, they are prone to leakage due to the inherent discontinuity in the linings of abutting duct segments. Leakage is particularly a problem when the mechanical clamp(s) work loose, e.g., due to vibration and other disturbances. What is needed are ducts, or more generally conduits, that may be installed or otherwise assembled in segments, but which have linings continuous across the joints between abutting segments.